1. Field of the Invention
The present invention relates to a polymer compound and a recording medium that can provide a recorded image free of discoloration or fading of the image caused by acid gases in the air or light and blurring of the image under a high-temperature and high-humidity environment and suitable for long-term storage when recording is conducted by means of a printer or plotter utilizing an ink-jet recording system.
2. Related Background Art
An ink-jet recording system is a system that minute droplets of an ink are applied to a recording medium such as paper by various working principles, and at the same time, a solvent component in the ink penetrates into the recording medium or evaporates, thereby precipitating a coloring material component in the ink on the recording medium to make a record of images, characters and/or the like (hereinafter referred to as “image”) and has such features that recording can be conducted at high speed and with a low noise, recording patterns are very flexible, multi-color images can be formed with ease, and development and image fixing are unnecessary.
In recent years, in particular, ink-jet printers have been rapidly widespread as image-recording apparatus for various kinds of information instruments, because an image formed by a multi-color ink-jet recording system has such merits that it can have quality comparable with an image formed by multi-color printing of a plate system or a color photography system, and that it is provided at a cheaper printing cost than that by the ordinary printing or photographic technique when the number of copies is small. Accordingly, the ink-jet printers are about to be widely applied to fields of which recording of full-color images is required, for example, outputting of image designs in design industries, production of color block copies in a printing field of which photographic quality is required, billboards and trade samples that are frequently replaced, and the like. Further, with the wide spreading of personal computers and digital still cameras, there have been recently many chances of outputting photographic images using an ink-jet printer even in domestic use.
However, the image recorded by the ink-jet printer is markedly faded or discolored by acid gases in the air and light compared with the images of the multi-color printing of the plate system and the color photography, and so such an image is unsuitable for an image, of which long-term storage is required, under the circumstances. Accordingly, there has been a very strong demand for prevention of the fading and discoloration of images formed by the ink-jet printers, and many proposals for improving such performance properties have been made to date.
For example, recording media containing a thioether compound in Japanese Patent Application Laid-Open No. 1-115677, a hydrazide compound in Japanese Patent Application Laid-Open No. 61-154989, or a thiourea derivative, thiosemicarbazide derivative, thiocarbo- hydrazide derivative or the like in Japanese Patent Publication No. 4-34953 and Japanese Patent Application Laid-Open No. 7-314883 are disclosed for the purpose of improving gas fastness. A recording medium containing one selected from a thiourea derivative, a thiosemicarbazide derivative and a thiocarbohydrazide derivative and one selected from iodine, an iodide, dithiocarbamic acid, a thiocyanate and a thiocyanic ester is disclosed in Japanese Patent Application Laid-Open No. 08-25796.
On the other hand, recording media containing a phenolic antioxidant and a benzophenone or benzotriazole type ultraviolet absorbent are disclosed in Japanese Patent Application Laid-Open Nos. 57-74192, 57-87989 and 60-72785 as recording media for improving light fastness of images.
In addition, a recording medium containing a hindered amine compound and a recording medium containing a hydrazide compound have been proposed in Japanese Patent Application Laid-Open Nos. 61-146591 and 61-154989, respectively.
Further, recording media with ascorbic acid, erysorbic acid or sodium erysorbate contained in an ink-receiving layer and with a flavonoid contained in an ink-receiving layer are disclosed in Japanese Patent Application Laid-Open Nos. 7-195824 and 8-150773, and Japanese Patent Application Laid-Open Nos. 2001-71627, 2001-139850 and 2001-301315, respectively, for improving the gas fastness and light fastness of images.
However, many of the above-described compounds are water-insoluble compounds and involve a problem that they cannot be added to an aqueous coating liquid for forming an ink-receiving layer. On the other hand, water-soluble compounds among the above-described compounds tend to make an image formed on an ink-receiving layer containing such a compound easy to blur under a high-temperature and high-humidity environment. When such a compound is added in a great amount to an ink-receiving layer for imparting sufficient gas fastness and light fastness to an image formed on the ink-receiving layer, the density of the image may be lowered in some cases.